1. Field of Technology
The present invention relates generally to an apparatus for detecting the residual energy of a battery installed in a device, and more particularly for detecting the residual energy of a battery installed in a mobile device in which the battery output differs depending upon the operating mode of the device. Such mobile devices include compact printers and digital cameras.
2. Description of Related Art
Various devices for detecting the residual energy (“remaining capacity”) of a battery installed in a mobile device are known from the literature. The device taught in Japanese Unexamined Patent Appl. Pub. H7-325134, for example, has a first voltage detector for detecting a discharge voltage greater than a threshold voltage, and a second voltage detector for detecting the threshold voltage, based on a threshold voltage determined according to the maximum discharge voltage of the battery. To detect the battery capacity, both the first and second voltage detectors detect the discharge voltage in respective detection ranges, and determine whether the detected discharge voltage is greater than the threshold voltage based on first and second digital values acquired from the detected discharge voltages. Based on the result of this comparison, either the first or second digital value is selected, and the residual battery capacity is determined based on the selected digital values.
This detection device improves the resolution of the analog/digital conversion circuit by using two different voltage detectors to detect the discharge voltage, and thereby improves the discharge voltage detection precision.
This detection device converts the detected discharge voltages of the battery to digital signals using an A/D converter, regularly samples the digital signals using the MPU in the device, and calculates the battery capacity based on predetermined rules.
In mobile devices such as compact printers, however, the battery load differs greatly between the printer mechanism when operating in a (high load mode) as compared to when the printer mechanism is in a standby state (low load mode). While the discharge voltage of the battery varies greatly with this change in the load, a heavy load is also applied to the MPU of the device when the printer mechanism is in the operating mode. It is therefore difficult to use the MPU to sample the battery discharge voltage. If the sampling interval is increased in order to reduce the load on the MPU, detection precision drops, and voltage detection may not be possible at the maximum discharge load.
Because the discharge voltage fluctuates greatly in the high load mode, there is a limit to the detection precision that can be achieved by sampling the A/D-converted digital discharge voltage signal at a constant period and processing the sampled values by the MPU.
Furthermore, when a compact mobile printer is monitored by a host device, communication is required between the printer and host at a regular timing. This means that the MPU must also have sufficient reserve capacity to handle communications. Because the operating mode of the compact printer is unrelated to the communication timing, the MPU must also have sufficient capacity to enable smooth communication even when the printer is in the high load mode.